1. Technical Field
The present invention relates in general to communication networks and, in particular, to an IP-centric communication network. Still more particularly, the present invention relates to an IP-based communication network including a network access system having distributed and separated routing, signaling, service control, filtering, policy control and other functionality from IP forwarding.
2. Description of the Related Art
The Internet can generally be defined as a worldwide collection of heterogeneous communication networks and associated gateways, bridges and routers that all employ the TCP/IP (Transport Control Protocol/Internet Protocol) suite of protocols to communicate data packets between a source and one or more destinations. As is well known to those skilled in the art, the TCP/IP suite of protocols corresponds to layers 3 and 4 (the network and transport layers, respectively) of the seven-layer International Organization for Standardization Open Systems Interconnection (ISO/OSI) reference model, which provides a convenient framework for discussing communication protocols. The ISO/OSI reference model further includes physical and link layers (layers 1 and 2, respectively) below the network and transport layers, and session, presentation, and application layers (layers 5 through 7, respectively) above the network and transport layers.
FIG. 1A illustrates a metropolitan level view of an Internet Service Provider (ISP) network 10 through which customers can access the Internet. Starting from the left hand side, many customer Local Area Networks (LANs) 14 interface to ISP network 10 via a variety of metropolitan access networks 16, which employ any of a number of network technologies; for example, Time Division Multiplexing (TDM), Asynchronous Transfer Mode (ATM), and Ethernet. Furthermore, as is typical in larger metropolitan areas, there are multiple levels of hierarchy in metropolitan access networks 16, with multiple rings connecting each customer to an aggregation site and multiple lowest level aggregation sites feeding a higher-level aggregation site. Typically, there may be only a few aggregation sites where aggregation routers 12 are deployed in a metropolitan area. FIG. 1A shows only one such aggregation site 17. All traffic from a customer LAN 14 is backhauled via these aggregation networks to this aggregation site 17, where aggregation routers 12 apply policy-driven treatment such as policing, marking, and admission control. Aggregation routers then route the traffic either back to another customer LAN 14, or else to core router 18 for transmission across core 20 to some more distant destination.
The state of the art in router design to a large extent dictates the network design shown in FIG. 1A because routers are expensive and must operate on highly aggregated traffic flows. A principal consideration in the design of such networks is to minimize the number of routers so that the routing protocol will scale effectively. This means that a number of functions are concentrated in these routers: routing, policy database storage, and policy enforcement.
In the prior art, router architecture is generally monolithic and proprietary. Consequently, the range of data services that a service provider can offer in addition to basic packet routing is limited by the control software offered by router vendors. In addition, the packet-processing throughput of a router is generally limited by its originally installed processing hardware and cannot be expanded or extended without replacement of the entire router. The monolithic and proprietary design of conventional routers presents a number of problems addressed by the present invention.
First, because routers traditionally have a single controller providing all services for all message types, edge router controllers tend to be quite complex, making it difficult and expensive to add new services or modify existing services. As a result, the time to market for new router-based services is extended and is usually dependent upon vendors responding to service provider requests to implement new services within their proprietary router architectures.
Second, conventional monolithic router architectures are not readily scalable, which presents a significant problem for service providers, particularly in light of the phenomenal growth of Internet traffic. Consequently, the processing capabilities of deployed routers cannot easily be scaled to keep pace with increasing traffic. Instead, service providers must purchase additional or replacement routers to meet the demands of increased traffic.
Third, conventional monolithic router designs also have limited flexibility and extensibility. For example, the present invention recognizes that it would be desirable, in view of the rapid growth of Internet traffic, to dynamically provision, configure, and/or reallocate access capacity to IP-based services. Because access capacity is necessarily limited and providing additional access capacity is a major cost component of networks, the enforcement of intelligent admission control policies and provision of differing qualities of service is vital to the efficient utilization of available access capacity. However, conventional edge routers are not capable of classifying a wide variety of traffic types while enforcing policy controls or of responding to dynamic requests for capacity, and this functionality is difficult to incorporate within currently deployed monolithic edge routers. The present invention accordingly recognizes that it would be desirable to provide the above as well as additional policy control, network monitoring, diagnostic, and security services in commercialized hardware, while permitting these services to be tailored to meet the needs of individual customers and service providers.
Fourth, because of the proprietary nature of router architectures and services, if a service provider deploys routers from multiple vendors in a communication network, the proprietary services implemented by the different router vendors will not necessarily inter-operate. Consequently, service providers are not able to purchase routers and switches from one vendor and purchase service control software from another vendor. Furthermore, a service provider cannot offer its communication network as a platform for a wholesale provider to offer value-added data services utilizing the existing base network capabilities.
In view of the foregoing and additional shortcomings in the prior art, the present invention recognizes that it would be desirable to introduce a new network access architecture that addresses and overcomes the limitations of conventional monolithic router architectures.